The depletion of the global stratospheric ozone shield is leading to a rise in the level of near-ultraviolet radiation (UVB-290-320 nm) reaching the earth's surface. Humans are also exposed to NUV radiation through the use of tanning beds. Increases in near-ultraviolet radiation are believed to be responsible for the dramatic rise in the incidence of skin cancer.: The overall objective of this lab is to identify specific biological mechanisms involved in the damage, protection and recovery from near- ultraviolet radiation. Escherichia coli will be used as a model organism to investigate the relationship between the genes that controls iron uptake (ferric uptake regulator; fur) and the stationary-phase sigma factor (rpoS). RpoS is a central regulatory component in bacteria for the defense against near-ultraviolet light (NUV; 290-400 nm). Hydroperoxidases, HPI and HPII, are members of the RpoS regulon. The specific aim of this study is to determine the levels at which Fur and RpoS interact to regulate cellular response to NUV irradiation and other stresses. If the Fur protein plays a key role in iron-dependent activation of rpoS regulon, mutants that affect the uptake, release and utilization of iron will be excellent genetic tools to determine the locations in the iron uptake and supply pathways that influence rpoS activity. This study will also determine whether the Fur protein is involved in an oxyR- dependent pathway regulating catalase activity. Catalase activity will be assayed at different phases of the cell's life. Utilizing oxyR and rpoS mutant strains that are known to regulate HPI and HPII at different stages of the cell's life cycle, we will be able to determine the role of Fur in contributing to the levels of HPI and HPII during both stationary and exponential phases. The effect of iron availability on the activity levels of HPI and HPII catalase will be determined in iron-rich and iron- deficient media. Regulation at the transcriptional level will be conducted using rpoS: :lacZ and katG::lacZ and katE: :lacZ promoter fusions. Overall this study will help identify other cellular conditions and genes that regulate RpoS activity, and unravel the complex mechanisms that regulate catalase synthesis and other cellular defense mechanisms against NUV radiation. This research will provide training opportunities in research for undergraduate students enrolled in pre-professional programs in optometry and pharmacy.